Hi @ShannonBiondi !
I hope you get in to this course, it sounds like a great skill to add to your illustration knowledge!
In my experience, portfolios should highlight your strongest works. In animation, I think they like seeing an idea executed from sketch to final where things like composition, setting, and character are explored. In traditional programs they like to see that you know how to bring a concept from sketch to final, have technical knowledge, and can neatly organize your work. Animation usually involves having a knowledge of how things move so I would submit a page of sketches of a moving target from life, some figure drawings perhaps to show an understanding of anatomy, and maybe something more rendered. Although this all depends on what kind of animation course this is, because if it's more graphic you can show storyboards of a shapes moving and morphing or a logo. It's all dependent on the work you're doing now.
I think in the end you should just make sure that whatever you submit can be understood clearly and that you have a variety of different work (showing a variety of mediums, subject matter, etc), which will then show that you've been experimenting and practicing. I would hold off on showing older work that doesn't express your skill level now though. I think showing off where you're at now is the way to go. Best of luck!